Sam the Science Kid Experiment 7: Density

Continuing my blogging project for 2011 where I do a science experiment per week with my seven year old daughter.

This week I continued rooting through the pantry for supplies, and decided to team Sam about density and why some things float. This was really simple as far as experiments go, but it turned out to be Sam’s favorite yet, plus I was able to get her sister Mandy involved as well. Here’s the supplies:

A tall glass

Water (I added red food coloring to mine)

Dishwashing soap

Cooking oil

An assortment of small objects that you don’t mind getting oily, oily and wet, or oily, wet, and soapy.

Any three (or more) liquids of different densities that don’t dissolve in each other would work, but these three worked for me. And yes, it’s too bad I couldn’t get them to go green, yellow, red like a traffic light, but I am unable to control the density of these liquids. FOR NOW.

Sam was extremely curious as to why the liquids separated out and didn’t mix, especially after I poured a bit of water on top and she watched it flow down through the oil to join the red layer:

I explained that the three liquids all had different densities, which kind of meant that they were more or less packed together in the same space. Denser liquids weight more than less dense materials, and less dense materials float to the top of denser ones. Sam seemed to get it and inspected the glass carefully while I had panicky premonitions of trying to clean up oil, soap, and water from the kitchen table:

The next part of the experiment was to drop various items into the glass and see where they settled. I explained that this would tell us how dense the objects were, since like the liquids the solids would float on top of anything that they were less dense than. The objects I gathered included a penny, a piece of carrot, a plastic bead, a rock, a marshmallow, a piece of potato, a Lego block, a piece of rubber, and a piece of macaroni. For the first few, I had Sam make predictions about how far down they’d sink, then I had her record her observations.

She absolutely loved doing this, and since this was an activity that basically involved dunking things in other things, Mandy was both able and willing to participate. I think part of the appeal here is that kids love making predictions and repeating trials with slightly different conditions. In this way, they’re natural scientists, and it’s not far removed from how babies learn to do, well, everything. When you’re a kid, most of what you encounter is new, and the only way to figure it out is to do trial after trial and make observation after observation.

Once they had exhausted my supply of small objects, they asked if they could find other stuff to drop in. When I said they could, the first thing Sam nominated was my iPod, which was one sacrifice I was not prepared to make for science. At any rate, not only did Sam love this, she proclaimed that it was the most fun experiment we had done to date. Here’s her journal entry in full:

Experiment 7: Density.
Things that are less density float on things that are more dense. I prdect the marshmallow will float on the oil. I prbekt that the rock will go to the dotem. The peanut floated in the water. The butt rock fell to the botem.

And, as a footnote, Sam did indeed write “The butt rock fell to the botem (sic).” She and Mandy have named the rock in question thus because a streak of quartz in the lower half of the rock does indeed look like a generous backside. Since it was for science, I allowed it.